1. Field of the Invention
This invention relates to a color temperature detecting device suited for the white balance adjustment device of a color TV camera which is arranged to detect the color components of illumination applied to an object and to automatically accomplish white balance adjustment according to the result of detection.
2. Description of the Related Art
White balance adjustment is one of the important signal adjusting actions for a color TV camera. The term "white balance adjustment" means variable adjustment of the gain, etc. of the chrominance signal of an object's image picked up to bring three primary color components (red, green and blue) into the ratio of 1:1:1 relative to a white object. The three primary color component ratio varies with the kind of illumination. Inadequate white balance adjustment makes color reproduction with fidelity impossible as it causes the whole picked up image plane to have a bluish or reddish appearance.
In view of this, a white balance device called an outside-detection automatic follow-up type white balance adjustment device has been contrived for accurately and automatically adjusting the white balance. Devices of this kind has been disclosed in Japanese Patent Applications Laid-Open No. SHO 54-53924 and SHO 55-158792, etc. These devices are arranged to detect the ambient light of the object by means of a light receiving system provided separately from an image sensing system and to automatically adjust the white balance on the basis of the result of detection. More specifically, two or three photo sensors, each having a color filter in front of it, are arranged to detect two or three different color components from the ambient light. These color components are logarithmically compressed. After that, differences among them are obtained. Then, ratios among the color components of the ambient light are equivalently detected. The gain of the chrominance signal amplifier of an image pickup (or sensing) system is controlled for white balance adjustment.
However, the conventional device of the above stated kind must be provided with a highly accurate logarithmic compression amplifier for adequately coping with ambient light having a wide ranged illuminance. In addition to that, the conventional device necessitates the use of a correction circuit for correction of temperature, etc.. These requirements thus have resulted in a complex arrangement and increased cost of the device.